Carbon brush for the collector current of electrical machines



G. CARBON BRUSH FOR THE COLLECTOR CURRENT OF ELECTRICAL MACHINES FiledOct. 13, 1959 INVENTOR gerrit star-re AGE- United States Patent Ofilice3,075,l l l Patented Jan. 22, 1953 3,ii75,111 CARBUBN RRUEH E052 THEQGLLECTQR CURRENT 9F ELEQTREHCAL MACHlNES Gerrit Stacie, Drachten,Netherlands, assignor to North American Philips Cernpany, inc, New York,N.Y., a corpcraticn of Delaware Fiied fi st. 13, 1959, Ser. No. 84d,176Claims priority, appiication Netherlands Oct. 14, 1953 4 Claims. (Cl.310-248) The invention relates to a carbon brush to establish thecontact with the collector of an electrical machine, particularly alow-power machine, such as used for dry shaving apparatus and ischaracterized in that the brush has a trapezium configuration.

According to a further feature of the invention the carbon brush isarranged in the electrical machine so that the trapezium section is atright angles to the collector surface, the base extending in thedirection of rotation of the collector.

This provides the advantage that the block brush can be utilized to thelast part. It has been found that the brush is subject to a maximum wearon the side where the collector or commutator laminations interrupttheir contact with the brush i.e. the trailing edge of the brush. Thisinvolves that the brush is worn oil? obliquely and will occupy anincreasingly more slanting position relative to the col ector surfaceuntil this is prevented by the wall of the tubular brush guide, so thatby further wear of the brush only one part of the effective brushsurface engages the collector. When the brush is almost completely used,the remainder is a piece of triangular section, of which the contactsurface decreases gradually and is therefore unserviceable. Thisremainder therefore means a loss of material. By rendering the brushhigher or thicker on the side of maximum wear than on the other side,which is obtained by the trapezium section, this drawback is obviated.

The invention will be described more fully with reference to theaccompanying diagrammatical figures.

HG. 1 shows a carbon brush according to the invention,

FIG. 2 shows a side view thereof in a brush guide, used with a fiatcollector and FIG. 3 shows the same used with a cylindrical collector.

FIG. 1 shows a block brush 1 with trapezoidal configuration. The arrow 2indicates the direction of rotation of the collector and the arrow 3represents diagrammatically the spring pressure exerted on the brush.

When a collector lamination located below the brush leaves the edge 4, aspark is locally produced, so that on this side the brush is worn offmore rapidly than at the edge 5.

The brush shown in FIG. 1 is suitable [for use in machines comprising afiat collector, which is shown in FIG. 2.

To a plate or dish 6 of insulating material, which is arranged on therotor shaft (not fully shown), are secured three fiat collectorsegments, of which two are designated by 7 and 8, which are separated byan air gap, 9. A thin plate 10 of electrically conductive material,arranged at right angles to the trapezium section and having an aperturethrough which the brush slides,

serves as a brush holder for each of the brushes (only one shown) andthe current is supplied or conducted away via the connection 11 by aspirallized blade spring 12. Such an arrangement is possible since theheight 13 (see FIG. 1) of the trapezium constitutes the largestdimension, so that the brush lies in fiat position on the collector, sothat there is no risk of tilting. The edge f the brush 1 prevents acomplete wear, by which the blade spring and/or the collector could bedamaged.

The end Wall of brush l1, in which is located the edge 4, (see FIGS. 1and 2), constitutes part of a circle, so that the contact surface of thebrushes can be made to remain always constant. However, this wall may beflat as is shown by the broken lines of FIG. 1.

Owin to the large contact surface and the low pressure per squarecentimetre, the wear both of the brush and of the collector is considerbly diminished. This is, of course, only possible, if the surface ofeach of the laminations is sufficiently large to permit the use of afiat brush. Collectors having at the most six laminations are suitable.

Finally, FIG. 3 shows a cylindrical collector 15 with a brush 1.

What is claimed is:

l. A carbon brush tor establishing contact with the collector of anelectric machine comprising a carbon body having a largest dimensionbetween the surfaces defining the leading and trailing edge thereof, andthe longitudinal side wall surface of said body in the plane normal tosaid collector defining a trapezium whereby the contact surface of saidbrush remains substantially constant with wear.

2. A carbon brush for establishing contact with a disk shaped collectorof an electric machine comprising a carbon body having a largestdimension between the surfaces defining the leading and trailing edgethereof, and the longitudinal side Wall surfaces of said body in theplane normal to said collector defining a trapezium whereby the contactarea of said brush with said collector remains substantially constantwith wear, a brush holder, said brush holder comprising a flat platehaving an aperture adapted to receive said body, said plate lying in aplane parallel with the said disc shaped collector, and stop meanscomprising a plate overlying said brush and extending beyond saidaperture whereby complete consumption of said brush by wear isprevented.

3. A carbon brush according to claim 1 wherein said brush ischaracterized by having a curvalinear surface at the trailing edgethereof.

4. A brush assembly according to claim 2 wherein said brush is urgedagainst said collector by spring means operatively associated with saidbrush guide.

References fitted in the file of this patent UNITED STATES PATENTS1,116,402 Ferguson Nov. 10, 1914 2,399,935 Morrill May 7, 1946 2,595,621West May 6, 1952 2,703,372 Savage Mar. 1, 1955 2,773,247 Erhardt Dec. 4,1956 FOREIGN PATENTS 369,366 Great Britain Mar. 24, 1932 521,453 FranceMar. 5, 192 1

2. A CARBON BRUSH FOR ESTABLISHING CONTACT WITH A DISK SHAPED COLLECTOROF AN ELECTRIC MACHINE COMPRISING A CARBON BODY HAVING A LARGESTDIMENSION BETWEEN THE SURFACES DEFINING THE LEADING AND TRAILING EDGETHEREOF, AND THE LONGITUDINAL SIDE WALL SURFACES OF SAID BODY IN THEPLANE NORMAL TO SAID COLLECTOR DEFINING A TRAPEZIUM WHEREBY THE CONTACTAREA OF SAID BRUSH WITH SAID COLLECTOR REMAINS SUBSTANTIALLY CONSTANTWITH WEAR, A BRUSH HOLDER, SAID BRUSH HOLDER COMPRISING A FLAT PLATEHAVING AN APERTURE ADAPTED TO RECEIVE SAID BODY, SAID PLATE LYING IN APLANE PARALLEL WITH THE SAID DISC SHAPED COLLECTOR, AND STOP MEANSCOMPRISING A PLATE OVERLYING SAID BRUSH AND EXTENDING BEYOND SAIDAPERTURE WHEREBY COMPLETE CONSUMPTION OF SAID BRUSH BY WEAR ISPREVENTED.